Tuesday, September 29, 2015

Big Signal Loop? Consider Using a Splitter.

Acromag Industrial Signal Isolated Transmitter
Industrial Signal Transmitters
Courtesy Acromag
Industrial process measurement and control requires the transmission of signals from point to point with no significant distortion. Even with the growing prevalence of wireless signal transmission, over-wire transmission of signals is still a primary means of connecting one device to another.
In the cabled process measurement and control world, the 4 to 20 milliampere signal is generally considered the standard for transmitting analog control and measurement signals over any distance.
There is an immense array of instrumentation and controllers available for use with 4-20 ma signals, so expertise in routing and delivering those signals should be part of your process M&C skill set.

Like just about everything else, routing 4-20 ma signals presents its own set of challenges that require some thought and planning to overcome. Electrical interference is always a concern and must be prevented from impacting the operation of measurement and control devices. Additionally, there must be sufficient power in the signal loop to accommodate the resistance load of connected devices. There are other considerations, but I'm going to focus on these two.

One scenario that can present significant issues is multiple devices requiring connection to the same signal, but with great distance between them. A simple solution can be implemented using an isolated signal splitter.

Features of these units making them an attractive, single box, solution:

  • One 4-20 ma input channel for the measuring or controlling device.
  • The input signal is retransmitted as identical isolated 4-20 ma signals
  • Galvanic isolation from input to output
  • Isolation between channels for safety and increased noise immunity. Fault in one output channel does not impact the operation of the other channels.
  • Reliable operation in industrial environments, with protection from RFI, EMI, ESD, and surges.
  • Low radiated emissions in accordance with CE requirements. 
  • DIN-rail mounting of the unit
  • Plug-in terminal blocks
If you have a very long signal loop, connecting multiple devices, consider breaking the devices into two groups that may allow for a substantially shorter cable length for each group. Connect each group to one of the isolated outputs of the splitter, giving each group of instruments the identical signal without the risks or impractically of an excessively long cable run.

There are other devices available that may combine special characteristics that solve your signal transmission challenges. Contact a product specialist and discuss your existing or anticipated project requirements. I continually urge engineers to take their process expertise, combine it with the extensive product knowledge of a professional sales engineer, and produce the best possible outcome.

Monday, September 21, 2015

Electric Power Where There Is No Grid

Humankind's quest to continually do more than has been done before takes engineers and technicians, along with their equipment, instruments, and other gear, to all corners of the Earth. Wherever the project goes, electric power will be needed to power it. Unless the needs are short term and very small, a reliable means to produce electric power on site must be put in place to operate equipment, instruments, and other systems necessary for the installation to function as needed.

The potential applications for remote power are vast, ranging from simple land based off-grid locations to ocean platforms, even polar stations. Industrial process measurement and control is found everywhere, which means that sometimes you need to provide the power to operate your own measurement and control equipment. To some, this will be a new challenge to their project management, design, or implementation skills.

Gentherm Global Power Technologies is not only the world leader in thermoelectric generation for remote power systems, they also employ solar and engine driven generator sets in their turnkey systems that can be specifically tailored to your application and installation site. As providers of a wide range of generation technologies, Gentherm is in a unique position to propose the most reliable and cost effective solution for each particular project. Become familiar with this company. You never know where your next project may be located.

A short video, included below, will get you started. You can also contact a product specialist to discuss any aspects of applying the technology.

Monday, September 14, 2015

Delivering Electric Power to Remote Sites

Thermoelectric Generator
Thermoelectric Generator
Courtesy Gentherm
Industrial companies accomplish some amazing feats in some very inaccessible and remote places. If you are in the natural resource business, you go where the resources are to extract them from the earth. The telecommunications industry locates equipment where needed to forge links and deliver signals. Environmental monitoring, navigation aids, buoys, lighthouses, and airstrips can all be situated in areas without grid power. Often, these installations are unattended, and require continuous reliable electric power to operate. When there is no grid to which the installation can be connected, a challenge arises regarding how to provide electric power to the site equipment.

There are several possible solutions for providing remote power, each with its own set of operating attributes which may make it more or less suitable for any particular application. When considering a remote power generator, you should include thermoelectric generators on your list of prospects.

Thermoelectric generators convert heat directly into electricity using a fuel source for heat, a hermetically sealed thermopile, cooling fins, and no moving parts. These generators are a positive and cost effective solution for remote power requirements, having operational and cost benefits over engine driven generators, batteries and solar sources for many applications.

The short document below provides an overview of thermoelectric generator operation and application. Talk to a product specialist about your need to power a remote site. A thermoelectric generator may be an option you had not considered, but may prove to be the best solution.

Monday, September 7, 2015

Practical Considerations for Thermocouple Selection

Industrial Thermocouples, Fixed Bend Bayonet Type
Industrial Thermocouples, Fixed Bend Bayonet Type
Courtesy Wika
It would be difficult to chart a career course in the industrial process control field without being exposed to thermocouples. They are the ubiquitous basic temperature measuring tools with which all process engineers and operators should be familiar. Knowing how thermocouples work, how to test them, is essential. Sooner or later, though, you may be in charge of selecting a thermocouple for a new application. With no existing part in place for you to copy, what are the selection criteria you should consider for your process?

Thermocouple sensor assemblies are available with almost countless feature combinations that empower vendors to provide a product for every application, but make specifying a complete unit for your application quite a task. Let's wade through some of the options available and see what kind of impact each may have on temperature measurement performance.

  • Thermocouple Type: Thermocouples are created using two dissimilar metals. Various metal combinations produce differing temperature ranges and accuracy. Types have standard metal combinations and are designated with capital letters, such as T, J, and K. Generally, avoid selecting a type that exhibits your anticipated measurements near the extremes for the type. Accuracy varies among thermocouple types, so make sure the accuracy of the selected type will be suitable.
  • NIST Traceability: This may be required for your application. The finished thermocouple assembly is tested and compared to a known standard. The error value between the thermocouple shipped to you and the standard are recorded  and certified. The certified sensor assembly will be specially tagged for reference to the standard.
  • Junction Type: If your sensor will be contained within a tube or sheath, the manner in which the actual sensor junction is arranged is important. The junction can be grounded to the sheath, electrically insulated from the sheath (ungrounded), or protruded from the sheath (exposed). If your process environment may subject the sensor assembly to stray voltages (EMF), it may be wise to stay away from a grounded junction, even though it provides fast response to a change in temperature. Exposed junctions provide very quick response, but are subjected to potential damage or corrosion from surrounding elements. The ungrounded junction provides protection within the enclosing sheath, with a slower response time than either of the other two junction types. When using ungrounded junctions, keep the mass and diameter of the sheath as small as might be practical to avoid overdamping the sensor response.
  • Probe Sheath Material: This applies to assemblies installed in a tube or sheath which houses and protects the sensor junction and may provide some means of mounting. Material selections include a variety of stainless steel types, polymers, and metals with coatings of corrosion resistant material to suit many applications. Make sure the sheath material, including any coatings, will withstand the anticipated temperature exposure range.
  • Probe Configuration: Sheath tube diameter and length can be customized, along with provisions for bends in the tube. Remember that as you increase the mass around the junction, or increase the distance of the junction from the point of measurement, the response time will tend to increase.
  • Wika Industrial Thermocouples, Various Termination Options
    Industrial Thermocouples, Showing Various Termination Options
    Courtesy Wika
  • Fittings and Terminations: There are innumerable possibilities for mounting fittings and wiring terminations. Give consideration to ease of access for service. How will the assembly be replaced if it fails? Are vibration, moisture, or other environmental factors a concern? What type of cable or lead wires would be best suited for the application?
Your options are so numerous, it is advisable to consult a manufacturer's sales engineer for assistance in specifying the right configuration for your application. Their product knowledge and application experience, combined with your understanding of the process requirements, will produce a positive outcome in the selection procedure.